Monitoring drift and associated biodiversity of nearshore rafts of holopelagic Sargassum spp. in the Mexican Caribbean

Abstract

Recent recurrent inundations of holopelagic Sargassum species (sargasso) in the tropical North Atlantic warrant studies to increase our understanding of this phenomenon. We carried out a multidisciplinary study to determine the drift and associated biota of sargasso rafts in nearshore waters of a reef system in the Mexican Caribbean, during the 2020–2022 influx seasons. Home-designed trackable drifting buoys revealed notorious influence of winds stronger than 4–5 m s⁻¹ on the rafts´ displacement. At lower wind velocities, the drift was almost entirely determined by currents; local topography played a role in concentrating or dispersing the algae. Video cameras attached to the drifting buoys allowed for non-invasive identification of free-swimming ichthyofauna, recording low specific richness with a dominance of species of the Carangidae family. Sargasso associated biota was sampled with a dipnet. The small motile macrofauna was abundant and diverse, with a dominance of few species. Epibionts (epifauna and epiphytic algae) showed low specific diversity, while the microbial communities were dominated by (potentially pathogenic) Vibro spp. Small motile macrofauna was the only biota group with new records for the study region. Differences among sampling events were observed in the associated community; suggesting large inherent variability of the rafts´ biota. The information on wind, coastal hydrodynamics and topography on the displacement of the sargasso rafts will allow for better predictions of strandings, and information on associated non-native biota or dominant microbial species helped identify groups that should be closely monitored; thereby aiding in targeted management actions for mitigating the impacts of the inundations.